it is working splendidly at the moment. i have played quite a bit with phase plug ideas… and with damping of the diaphram. at some point soon i will go into the history of what you see here, but for now i will just add pix. because i use a current amp (transconductance amplifier: voltage signal in, linear current out) to drive these, i have also made a network, an RLC filter, to help equalize the resonant peak in the lower frequencies. this adds a margin of safety for the drivers, which are fragile, as well as allows some opportunity for leveling the lower frequencies. this speaker comfortably reaches 80Hz with an amp that is good for 10 watts. the network has a wirewound pot to adjust the “damping” (not exactly the right word) somewhat.
here is a larger profile that helped a lot at distance… this was an earlier attempt. i use these nearfield, so the smaller deflector worked better. i tried to find a “spaulding”, which for aesthetic reasons, means a lot to me. you can take the boy out of the street, but can you take the street out of the boy?
i have also added an RLC filter to equalize the impedance peak at resonance. here is an image of the arrangement, below. you may appreciate that the use of a wirewound pot allows for a certain amount of adjustment… it is interesting to play with it while listening. the little transconductance amps i have been playing with definitely need some help down low to limit the rise in output. but the effect is not exactly experienced as simply eq or “damping”… i’d be curious as to what other people hear?
in any case, the filter is a necessary part of this design. the small sealed box does protect the manger somewhat, and you can leave some “boost” in place to extend the low frequency perfomance of the driver, but in order to safely use 20 watt or 30 watt amps with this setup, the peak needs to be controlled somehow. the resonant frequency of the Manger driver is around 80 Hz in free air, and this will change a bit with the sealed box volume and the stuffing. best is to measure your driver in the baffle, and adjust the RLC to best fit.
and here is an image of how it is installed in the lower cabin of the salad days speaker… “salad days”, by the way, was one of my favorite monty python skits.
the optimum resistance will vary from box to driver but expect somewhere between 10 and 15 ohms typically, for an amp with a 60 ohm output impedance (what i am currently working with).
i really like the aircore inductors made by volt, in the UK. (i really like all of david’s stuff. i have some of his radial woofers for a big monitor…) you can see the 22mH one i ordered. it is big. the caps are metalized polypropelene and just okay. i didn’t have the room for the russian paper and oil ones i like. but, i believe it all worked out. one needs to know when to stop and move on.
and finally… IKEA makes a little storage box made of MDF and bamboo plywood. “VARIERAR”, it’s called. a pair of them, and a bit of plywood can make a lovely speaker box for a fair price. much less work than the salad bowls to modify, and yet still very satisfying…
these are also fitted for manger drivers. there is enough room inside for the RLC filter as well as a surface to mount a diffusor… it never ends, does it?